This invention relates to housings for industrial heat recuperators, and more particularly relates to a heat recuperator assembly employing a ceramic cross-flow heat recuperator for use on furnaces, ovens and preheaters in an improved housing.
Recent concern about energy conservation and rising fuel costs has caused renewed interest in industrial recuperators to recover waste heat losses and preheat incoming combustion air to increase the efficiency of furnaces, ovens, and preheaters.
While such recuperators are usually constructed from metal parts, the ceramic recuperator has several advantages over conventional metallic recuperators. For example, ceramics in general have high corrosion resistance, high mechanical strength at elevated temperatures, low thermal expansion coefficients (TEC'S) and good thermal shock resistance, and thus exhibit excellent endurance under thermal cycling; are light in weight (about 1/3 the weight of stainless steel); and are cost competitive with high temperature alloys.
Furthermore, ceramic recuperators are available in a variety of shapes, sizes, hydraulic diameters, (hydraulic diameter is a measure of cross-sectional area divided by wetted perimeter) and compositions. Because their TEC'S are typically lower than those of most metals and alloys, however, ceramic recuperators present a compatability problem to the design engineer desiring to incorporate them into existing furnace, oven and preheater structures.
In U.S. Pat. No. 4,083,400, issued Apr. 11, 1978 and assigned to the present assignee, a ceramic cross-flow recuperator core is incorporated into a metallic housing adapted for retrofitting to the metallic fittings of existing furnaces, ovens and preheaters. Insulating and resilient sealing layers between the core and housing minimize heat loss through the metallic housing and prevent leakage of heat transfer fluids, such as exhaust flue gasses and incoming combustion air, past the core.
Experience to date has shown that it is difficult to fabricate a unitary housing to the close tolerances needed to maintain a leak-free seal between the ceramic recuperator core and the housing. In addition, such unitary housings cannot be adjusted in size to accomodate different thermal expansions of the metal and ceramic in changing thermal environments.